1. Field of the Invention
The present invention relates to control devices for motor vehicles, and more particularly, to techniques for improving fuel efficiency of a motor vehicle provided with an idling stop controller and a neutral-at-idle controller.
2. Description of the Related Art
An idling stop controller has conventionally been known as a means of improving fuel efficiency of a motor vehicle, whereby the operation of an internal combustion engine is stopped when the vehicle stops moving such as at an intersection.
When a predetermined stopping condition is fulfilled as in a situation where the vehicle is standing at an intersection, for example, the idling stop controller automatically stops the idling of the engine. When a predetermined restarting condition is fulfilled thereafter, the idling stop controller restarts the engine so that the vehicle can be moved.
There has also been known a neutral-at-idle controller as a means of improving fuel efficiency of a vehicle.
When a predetermined shift-into-neutral condition is fulfilled during idling of the engine, the neutral-at-idle controller automatically shifts the transmission into neutral, to thereby improve fuel efficiency during idling.
There has been proposed a motor vehicle which is provided with both the idling stop controller and the neutral-at-idle controller and in which these controllers are selectively operated in accordance with the gradient of the road surface (Japanese Laid-open Patent Publication No. 2009-264513). For example, if the gradient of the road surface is relatively small, the idling stop controller is selected, and if the gradient of the road surface is relatively large, the neutral-at-idle controller is selected. Such a control method permits the fuel efficiency to be satisfactorily improved by the idling stop controller when the gradient of the road surface is relatively small, and to avoid stoppage of the engine and restrain lowering of the brake pressure when the gradient of the road surface is relatively large.
In the case of motor vehicles provided with both the idling stop controller and the neutral-at-idle controller like the one disclosed in the aforementioned publication, the stopping condition for activating the idling stop controller includes a conditional state which, when fulfilled, causes no problem regarding restart of the engine even if the engine is stopped, such as the state of charge of battery. Generally, therefore, the stopping condition is less likely to be fulfilled than the shift-into-neutral condition.
As a consequence, a situation occasionally arises wherein, immediately after the vehicle is stopped, the shift-into-neutral condition is fulfilled first, so that shifting into neutral is executed, and then the stopping condition is fulfilled, followed by automatic stop of the engine. If such a switchover of control mode from the neutral-at-idle controller to the idling stop controller takes place, a time lag is caused by the switchover, and thus it is difficult to execute automatic stop of the engine in a moment even if the stopping condition is fulfilled immediately after the shift-into-neutral condition is fulfilled. A problem therefore arises in that automatic engine stop by the idling stop controller, which provides a superior fuel efficiency improving effect, fails to be promptly executed immediately after the vehicle is stopped.